[CodeGen] Implement [[likely]] and [[unlikely]] for while and for loop.

The attribute has no effect on a do statement since the path of execution
will always include its substatement.

It adds a diagnostic when the attribute is used on an infinite while loop
since the codegen omits the branch here. Since the likelihood attributes
have no effect on a do statement no diagnostic will be issued for
do [[unlikely]] {...} while(0);

Differential Revision: https://reviews.llvm.org/D89899

1 files changed, 9 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 77b2c97..f1fe8f9 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -2555,3 +2555,12 @@ llvm::MDNode *CodeGenFunction::createBranchWeights(Stmt::Likelihood LH) const {
   llvm::MDBuilder MDHelper(CGM.getLLVMContext());
   return MDHelper.createBranchWeights(LHW->first, LHW->second);
 }
+
+llvm::MDNode *CodeGenFunction::createProfileOrBranchWeightsForLoop(
+    const Stmt *Cond, uint64_t LoopCount, const Stmt *Body) const {
+  llvm::MDNode *Weights = createProfileWeightsForLoop(Cond, LoopCount);
+  if (!Weights && CGM.getCodeGenOpts().OptimizationLevel)
+    Weights = createBranchWeights(Stmt::getLikelihood(Body));
+
+  return Weights;
+}